1. Field of the Invention
The present invention discloses an adjustable voltage comparing circuit and an adjustable voltage examining device, and more particularly, an adjustable voltage comparing circuit and an adjustable voltage examining device for confirming whether an audio signal under test is normal or not by examining whether a voltage level of the audio signal under test is between an high-threshold reference voltage and a low-threshold reference voltage or not.
2. Description of the Prior Art
Please refer to FIG. 1, which illustrates a conventional audio testing module 100. As shown in FIG. 1, the audio testing module 100 includes a logic tester 110 and a device under test 120. The logic tester 110 is used for issuing an input signal for testing, and for examining whether the device under test 120 is precisely operated or not according to a signal under test returned by the device under test 120.
The logic tester 110 may examine the device under test by two means. In a first means, a function generator of the logic tester 110 generates an input signal required by integrated circuits of the device under test 120; after a corresponding output signal, i.e., a signal under test, is generated from the device under test 120, a precision measurement unit of the logic tester 110 retrieves a measure value by measurements and calculations so as to examine whether the device under test 120 is precisely operated or not. However, during the examining procedure of the logic tester, interrupts have to be continuously issued for transferring tokens between the function generator and the precision measurement unit, so as to repeatedly set and generate different input signals; as a result, the testing procedure of the logic tester 110 cannot be synchronous, and a large amount of testing time and capitals is also wasted by the continuously-issued interrupts.
In a second means, just the function generator of the logic tester 110 is used for performing outputting and comparison related to the input signal and the signal under test, where there are comparators in the function generator for performing the required comparisons. Since the device under test 120 is able to use different gains for generating voltages of different voltage level ranges, different upper/low-threshold voltages have to be set for the generated voltages of different voltage level ranges; in other words, during the examination of the logic tester 110, the low/high-threshold voltages have to be repeatedly reset and loaded into comparators of the function generator for being compared with the signal under test, and large amounts of testing time is also wasted during the repeatedly reset operations and loadings.